This invention relates to an anode electrocatalyst composed of an alloy essentially consisting of at least one of tin, germanium and molybdenum, and one or more noble metal employed as an anode of a fuel cell and its preparation.
A solid polymer electrolyte fuel cell attracts more attention as an electric power source of an electric automobile and a space craft compared with a phosphoric acid fuel cell because it is compact and may take out high current density. Various electrode structures, preparations of catalysts and systems utilizing these catalysts and electrodes have been proposed.
The electrode structure of a conventional fuel cell is ordinarily a five-layered sandwich structure which consists of a cathode current collector, a cathode, a solid polymer electrolyte (ion exchange membrane), an anode and an anode current collector.
Fuel supplied to this fuel cell is prepared by means of, for example, reforming methanol, which contains carbon dioxide and carbon monoxide other than hydrogen. As an anode of the fuel cell, a substrate composed of a gas permeable carbon textile or the like carrying platinum metal catalyst particles and/or platinum-supporting catalyst particles consisting of carbon black and platinum metal catalyst particles supported thereon together with perfluorocarbon sulphonic acid and polytetrafluoroethylene (hereinafter referred to as "PTFE") formed as a layer has been frequently employed. However, the platinum and the platinum-supporting catalyst are liable to be poisoned with the carbon monoxide contained in the above fuel especially in the solid polymer electrolyte fuel cell which operates in a low temperature, to considerable lower the catalytic activities.
In order to overcome these drawbacks, pure hydrogen is desirably employed as fuel, but the pure hydrogen is not only expensive but also costly in its storage. For example, liquid hydrogen is liable to be scattered from a storage tank into air so that its storage is technically difficult. If the carbon monoxide is removed from the fuel prepared by the reforming of the methanol, no poisoning takes place as the pure hydrogen is supplied from the tank. However, the carbon monoxide is difficult to be completely removed from the fuel by means of a multistage treatment, and moreover this treatment is costly the same as the employment of the pure hydrogen.
Conventionally, the poisoning of the fuel cell electrode with the carbon monoxide has been the more important subject to be avoided in this field. The poisoning is a serious obstacle against the practical use of the fuel cell. In spite of various electrode materials, no fuel cell electrode has been developed which possesses a sufficient resistance to the poisoning.
Although a catalyst containing tin and a noble metal has been proposed (for example, Japanese patent laid open gazette No. 3-42040), it is intended to be employed for treating poisonous gases and consists of tin and a noble metal coated on the tin.